In monkey and man, inferotemporal cortex is necessary for normal visual learning and perception. Removal of this area in the monkey produces a severe impairment in visual discrimination learning, but does not affect visual thresholds, or discrimination learning in other modalities. We have shown that inferotemporal neurons usually have large receptive fields that extend well into both visual half-fields and often have complex trigger features. We will continue to study these neurons in both anesthetized and behaving monkeys with emphasis on their complex trigger features and on variations in their properties within inferotemporal cortex. Inferotemporal cortex may be a major mechanism for perceptual constancies and equivalences. For example, removal of inferotemporal cortex impairs the perceptual equivalence of patterns in the two visual half-fields. It also eliminates the equivalence of lateral mirror image stimuli shown by normal animals. In further experiments on the behavioral effects of inferotemporal lesions we will examine whether this area plays a more general role in perceptual constancies. The visual responsiveness of inferotemporal neurons depends on input from striate cortex by way of synapses in circumstriate cortex. The function of circumstriate cortex will be studied in electrophysiological, anatomical, and lesion experiments.